Aldehyde fixed tissue from monkey (Macaca mulatta) corpus luteum was incubated in alkaline 3,3'-diaminobenzedene (DAB), and prepared for electron microscopic histochemical observations. The objective of this study was to characterize the complex relationship of microperoxisomes and the agranular endoplasmic reticulum (AER) in the granulosa lutein cells. Out of the 107 microperoxisomes that were reconstructed from serial sections, 106 were directly joined to the AER. Two distinct forms of attachment were found between the AER and the microperoxisomes. In addition to the two types of connections, fine thread-like structures were observed extending between AER and adjacent microperoxisomes. BIBLIOGRAPHIC REFERENCE: Gulyas, B.J., Yuan, L., Tullner, W.W. and Hodgen, G.D.: The fine structure of corpus luteum from intact, hypophysectomized, and fetectomized pregnant monkeys (Macaca mulatta) at term. Biol. Reprod. 16: 613-626, 1976.